The long-term goal of this proposal is three-fold: (a) to learn about the natural history of chronic epileptogenic processes by comparative examination of chronological electroclinical features in both idiopathic and experimentally-induced focal epilepsy in subhuman primates; (b) to study neurobiological mechanisms underlying progressive seizure development in rats, cats, monkeys and epileptic baboons; and (c) to develop insight into rational strategies for prevention, based upon pharmacological manipulation, biochemical exploration and surgical lesioning of experimental models of epilepsy. This proposal is concerned with epileptic baboons (Papio papio and Papio cynocephalus). Our major effort will be directed towards clarifying the nature of epileptogenic predisposition in baboons. Further studies will aim at examining seizure susceptibility and general cerebral excitability, functional anatomy of progressive seizure development, unit and evoked potential activity associated with seizure development, the effect of surgical lesioning involving cortical and subcortical structures and of stimulations of nonspecific thalamic and reticular systems, and morphological changes which might be present in animals with recurrent spontaneous seizure state. In addition, pathophysiological mechanism of baboon's photosensitivity will be examined at various levels, including single unit activity in the brain stem, pattern sensitivity and subcortical stimulation. Finally, investigation of the effects of established and potential anti-epileptic drugs upon the development of seizures will be performed in order to obtain a comprehensive profile of the potential prophylactic effects of antiepileptic drugs.